Such a flushing valve arrangement is used for example in hydrostatic travel drives in which two hydromachines are operated in a closed hydraulic circuit. Via the flushing valve arrangement, pressurized medium is taken from the respective low-pressure branch of the closed hydraulic circuit in order to discharge heat and dirt particles from the circuit. The flushed pressure medium quantity is replaced by pressure medium fed in through the low-pressure branch, wherein a fixed low pressure of for example 30 bar must be maintained by infeed into the low-pressure branch. Normally, the flushing piston moves above a pressure difference of around 5 bar between the high-pressure branch and the low-pressure branch of the closed hydraulic circuit.
For example, DE 10 2005 051 324 A1 describes a hydraulic flushing valve arrangement having a flushing valve with a flushing piston, the two control collars of which towards the piston neck are provided with three flattenings which are evidently distributed evenly over the periphery of a control collar and open towards the piston neck. The flattenings extend to the diameter of the piston neck and terminate axially in a face standing perpendicularly on the axis of the flushing piston. In the circumferential direction between the flattenings, axial webs are present which are very narrow at the diameter of a control collar. As a result, the design of the control collars of the flushing piston known from DE 10 2005 051 324 A1 ensures that, after opening a fluidic connection between an inlet channel and the outlet channel, the flushing piston is still guided at the corresponding control collar, namely by the webs present between the flattenings. The control edge of a control collar is consequently axially level with the closed ends of the flattenings.
DE 10 2011 119 427 A1 discloses a flushing valve arrangement in which the flushing piston of the flushing valve moves against the force of a spring on small pressure differences of up to for example 40 bar between the two inlet channels, to reach and remain in a position in which the circular control edge of a control collar only has a small distance from the corresponding housing control edge. On greater pressure differences, the flushing piston is moved against the additional force of a second spring, which is higher than the force of the first spring, into a position in which a large axial distance exists between the two said control edges.
DE 103 15 512 B4 discloses a flushing valve arrangement in which the flushing piston is clamped in floating fashion between two springs which have a limited extension travel in one direction. Thus—disregarding friction—the flushing piston moves even on very small pressure differences between the two branches of the closed hydraulic circuit, wherein the gradient of the travel/force curve of the flushing piston to an end of the extension travel of a spring is twice the spring constant of the spring. The control collars of the flushing piston have a portion with a diameter corresponding to the valve bore and ending at a first circular control edge, and towards the inside a second portion with a slightly reduced diameter and with a second circular control edge.